1. Field of the Invention
This invention relates to cannon-launched projectiles or similar airborne vehicles. More particularly, this invention relates to apparatus and methods for searching for, tracking and remotely guiding cannon-launched projectiles, rockets and similar airborne vehicles to impact a selected target.
2. Description of the Prior Art
It was well-recognized in the prior art that a cannon-launched projectiles followed a ballistic trajectory which could be fairly well calculated. This knowledge enabled a gunner to fire projectiles to impact pre-selected target areas with reasonable consistency.
It also was known in the prior art to use land based apparatus to search the space in which the cannon-launched projectiles or rockets were expected to appear (known as object space) and thereafter locate and track such projectiles while they were in flight. The purpose of such prior art systems was to aid artillery and rocket launch batteries in obtaining greater accuracy by noting deviations from the expected trajectories of tracked projectiles, resulting from wind, weather or other reasons. The artillery or launch battery, when given the precise flight details of an actual projectile, could then adjust its aim in subsequent salvos.
Such prior art systems utilized active radar, usually in the frequency range of 12.5 to 18 Gigahertzs, to search object space. The reflected signal from the in-flight projectile was detected by the radar's receiving antenna. Then, a polar coordinate procedure could be used to track the in-flight projectile's path.
The search operation of such prior art systems was usually conducted by scanning the radar antenna mechanically in either a conical pattern or a raster pattern. The mechanical scanning mechanisms would be servo-controlled very precisely so that correct antenna positions could be achieved and/or noted.
The radar continuously emitted a beam of energy at power levels sufficient to produce a perceivable reflection from the flying projectile. Such power levels varied according to range, weather and the target's radar cross-section. Once a target of interest had been located, the search pattern would cease and the mechanized radar would then enter into a track pattern.
In order to maintain its track of a projectile, the radar had to continuously emit a signal commonly referred to as a beam. The track data, once acquired, was fed into the existing system's computer for further processing and relay to the user, such as the battery command center.
There have been many difficulties with these prior art apparatus. Mechanical systems of the proper sensitivity were so fragile that they proved unsuitable for field use and included many inherent errors which were difficult to detect. Additionally, reflections could vary greatly from one projectile to another because of, e.g., back scatter from rain, other scintillations, tilt of the projectile with respect to the beam, multipath reflections and the like.
Such prior art systems were also limited by their inability to search for and then track many projectiles at the same time because of mechanical limitations and the similarity of the reflected signatures from various projectiles. Mechanical systems, in order to have an acceptable degree of reliability, had to be made a size and weight which tended to increase manufacturing and selling costs prohibitively. Additionally, prior art tracking systems were subject to inaccuracies caused by round-to-round physical variations and time variant meteorological phenomena.
The present applicant has attempted to address some of these problems by disclosing improved imaging methods for the remote tracking systems. These systems involve fast framing thermal imaging systems comprising mechanical scanning devices for converting radiation in the far infrared spectral region to visible radiation in real time and at an information rate comparable to that of standard television. Such systems are commonly referred to as FLIR systems, the acronym for Forward Looking Infrared, and enable trackers in the field to effectively track projectiles when visually obscured by dust, darkness, or other environmental conditions.
These systems are disclosed in:
U.S. Pat. No. 4,407,464 PA2 U.S. Pat. No. 4,453,087 PA2 U.S. Pat. No. 4,886,330
all issued to the present applicant, James Linick.
Obviously, a major disadvantage of the cannon-launched projectile is the inability to control its trajectory after launch. One proposed control method would have incorporated a special signal within a radar carrier frequency which would have provided the projectile with guidance in the form of a midcourse correction. To date, such concepts have not become operational.
Another method, disclosed in U.S. Pat. No. 4,679,748 issued to Blomquist and Linick, discloses a cannon-launched projectile scanning and guidance system completely self-contained within the projectile itself. This system suffers from the inability of trackers at the artillery or launch battery to initiate control over the trajectory of the shell once flight has commenced.
Therefore, it is an object of the present invention to provide an apparatus and method which overcome the afore-mentioned inadequacies of the prior art devices by providing the improvement of searching for the projectile and then tracking and assisting in the remote guidance of weapons projectiles such as cannon and mortar launched projectiles, rockets and the like.
Another object of this invention is to provide a means to search the space in which the tracker expects the projectile to appear or object space by electronically intensive means rather than mechanically intensive means, thereby adding reliability, operation speed, lower physical weight and lower manufacturing costs.
Another object of this invention is to allow the ground-based apparatus to be substantially passive rather than continually active, thereby far more effectively maintaining the secrecy of the ground-based apparatus' location and, additionally, the battery cf artillery or rockets or the like to which it provides data.
Another object of this invention is to provide means to search for, locate and track multiple projectiles or rockets or the like simultaneously, thereby adding to the versatility of the system and eliminating the need for many systems when one will be effective.
Another object of this invention is to permit more readily and discreetly, and in a more usable form, the transmission of guidance commands to flying projectiles or rockets or the like.
Another object of this invention is to permit clear communication between the ground-based apparatus and the airborne apparatus at extended and pre-planned ranges.
Another object of the invention is to provide a means of round-to-round inflight trajectory correction.
The foregoing has outlined some of the more pertinent objects of the invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the invention. Many other beneficial results can be obtained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description of the preferred embodiments below.